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      <title>12、ThreadLocalMap - 交互式测验</title>
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    </head>
    <body>
      <div class="main-wrapper">
          <div class="quiz-container">
            <div class="quiz-header">
              <h1>12、ThreadLocalMap - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
            </div>
            <div id="quiz-content">
                <div class="quiz-body">
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                    <div id="question-container">
                      <p id="question-text"></p>
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      </div>

      <script>
        const quizData = [
  {
    "question": "根据文档，ThreadLocal能够实现线程隔离的核心原理是什么？",
    "options": [
      "ThreadLocal对象内部维护一个从线程ID到值的并发映射表。",
      "数据实际上存储在每个Thread对象内部的ThreadLocalMap中，而不是ThreadLocal对象本身。",
      "通过对全局变量加锁，确保同一时间只有一个线程可以访问。",
      "每个线程创建ThreadLocal对象时都会得到一个物理上独立的副本。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "ThreadLocal实现线程隔离的关键在于，每个线程（Thread对象）都有一个自己的成员变量`threadLocals`，它是一个ThreadLocalMap。当调用ThreadLocal的set或get方法时，实际上是在操作当前线程的这个私有Map，以ThreadLocal实例为键，存储的值为值。数据与线程绑定，从而实现了隔离。",
    "source": "文档中「4.1 ThreadLocal.set方法实现」部分",
    "hint": "文档中提到：关键点在于，ThreadLocalMap实例是存储在Thread对象中的，而不是..."
  },
  {
    "question": "在ThreadLocalMap的内部实现中，Entry的键（Key）为什么被设计成弱引用（WeakReference）？",
    "options": [
      "为了确保当ThreadLocal对象不再被外部引用时，其对应的value也能被自动垃圾回收。",
      "为了提高哈希表的查询性能，因为弱引用的访问速度更快。",
      "为了让垃圾回收器可以在ThreadLocal对象没有外部强引用时回收它，从而避免ThreadLocal对象本身的内存泄漏。",
      "为了节省内存空间，因为弱引用比强引用占用更少的内存。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "使用弱引用的核心目的是为了解决ThreadLocal对象本身的泄漏问题。如果使用强引用，即使外部代码已经不再持有对ThreadLocal实例的引用（例如，方法栈中的局部变量被销毁），但只要线程还存活，ThreadLocalMap就会一直持有该实例的引用，导致它无法被垃圾回收。弱引用则打破了这种强依赖，允许GC在没有其他强引用的情况下回收ThreadLocal对象。",
    "source": "文档中「1.3 弱引用键的设计理念」部分",
    "hint": "思考一下，如果Entry中的Key是强引用，当外部对ThreadLocal的引用消失后会发生什么？"
  },
  {
    "question": "ThreadLocal最常见的内存泄漏场景的根本原因是什么？",
    "options": [
      "ThreadLocalMap中的Entry的键（key）是弱引用，而值（value）是强引用。当key被回收后，value仍然存在，且无法被访问到。",
      "线程池中的线程永远不会被销毁，导致ThreadLocalMap无限增大。",
      "ThreadLocal对象本身是强引用，导致它永远无法被垃圾回收。",
      "调用remove()方法会破坏ThreadLocalMap的内部结构，导致数据丢失。"
    ],
    "correctAnswerIndex": 0,
    "explanation": "内存泄漏的根源在于Entry的结构：`key`是弱引用，`value`是强引用。当外部不再有对ThreadLocal对象的强引用时，GC会回收它，导致Entry中的`key`变为`null`。然而，`value`仍然被Entry对象强引用，而Entry对象又被ThreadLocalMap强引用，ThreadLocalMap又被Thread对象强引用。如果线程生命周期很长（如线程池），并且没有调用`get`、`set`或`remove`来触发清理机制，这个强引用的`value`就永远不会被回收，从而造成内存泄漏。",
    "source": "文档中「5.1 为什么会发生内存泄漏」部分",
    "hint": "文档中描述了这样的引用链：Thread实例 -> ThreadLocalMap -> Entry -> value。"
  },
  {
    "question": "当在ThreadLocalMap中发生哈希冲突时，它采用哪种策略来解决？",
    "options": [
      "使用链表法，将哈希值相同的Entry链接在一起。",
      "使用开放地址法中的线性探测，向后查找下一个可用的槽位。",
      "立即对整个哈希表进行扩容和重新哈希（rehash）。",
      "使用红黑树来组织哈希值冲突的Entry，以优化查询性能。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "文档中的源码和说明都明确指出，ThreadLocalMap在解决哈希冲突时，并未使用HashMap中常见的链表或红黑树，而是采用了开放地址法中的线性探测策略。即当计算出的槽位已被占用时，它会通过`nextIndex`方法顺序地检查下一个槽位，直到找到空位或目标Entry。",
    "source": "文档中「2.3 解决哈希冲突的策略」部分",
    "hint": "文档中提到：与HashMap使用链表或红黑树解决冲突不同，ThreadLocalMap使用..."
  },
  {
    "question": "根据文档，以下哪项操作不是ThreadLocalMap内部清理“陈旧Entry”（stale entry）的触发时机？",
    "options": [
      "当调用`set`方法，并且在寻找槽位过程中遇到一个key为null的Entry时。",
      "当一个线程长时间处于空闲状态，未执行任何ThreadLocal相关操作时。",
      "当调用`remove`方法移除一个Entry时。",
      "当哈希表大小达到扩容阈值，准备`rehash`时。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "文档中详细列举了清理机制的多个触发时机，包括调用`set`、`get`、`remove`以及`rehash`（扩容）时。这些清理都是在对ThreadLocalMap进行主动操作时“顺便”触发的。如果一个线程进入长时间的空闲状态，并且不再调用任何ThreadLocal的方法，那么即使其中存在key已被回收的“陈旧Entry”，自动清理机制也不会被触发。",
    "source": "文档中「5.4 清理机制的触发时机」部分",
    "hint": "文档强调：'必须有人调用ThreadLocalMap的方法才会触发清理'。思考哪个选项描述了'无人调用'的情况。"
  },
  {
    "question": "在ThreadLocal的哈希值计算中，`HASH_INCREMENT = 0x61c88647`这个“魔数”的作用是什么？",
    "options": [
      "它代表了ThreadLocalMap的初始容量。",
      "它是一个斐波那契散列乘数，用于生成均匀分布的哈希码，以减少冲突。",
      "它是一个位掩码，用于从哈希码中计算出在数组中的索引位置。",
      "它是ThreadLocalMap扩容时的增长因子。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "文档中明确指出，`0x61c88647`是一个特殊的“神奇数字”，它与黄金分割比有关，被称为斐波那契散列乘数。使用这个固定的增量来生成每个新的ThreadLocal实例的哈希码，可以使得哈希值在2的幂次长度的哈希表中分布得非常均匀，从而有效减少哈希冲突的概率。",
    "source": "文档中「2.2 哈希表设计」部分",
    "hint": "文档中称这个数字为'神奇的数字'，并解释了它能使哈希值'均匀分布'。"
  },
  {
    "question": "为了在线程池环境中安全地使用ThreadLocal并防止内存泄漏，最佳实践是什么？",
    "options": [
      "在任务代码的`finally`块中调用`ThreadLocal.remove()`方法。",
      "在任务结束时，将ThreadLocal变量赋值为`null`。",
      "什么都不做，完全依赖ThreadLocalMap内置的自动清理机制。",
      "增加线程池的核心线程数，以减少线程复用带来的问题。"
    ],
    "correctAnswerIndex": 0,
    "explanation": "由于线程池中的线程会被复用，一个任务结束后，线程并不会销毁。如果不手动清理ThreadLocal变量，那么上一个任务设置的值会保留在该线程的ThreadLocalMap中，这不仅会造成内存泄漏，还可能被下一个使用该线程的任务错误地读取，导致逻辑错误。因此，最安全、最可靠的做法是在任务执行完毕后，在`finally`块中显式调用`remove()`方法，确保与任务相关的线程局部变量被彻底清除。",
    "source": "文档中「4.3 ThreadLocal.remove方法实现」及「5.4 清理机制的触发时机」部分的结论",
    "hint": "文档结尾处强调：'最安全的做法仍然是在不再需要ThreadLocal变量时，显式调用remove方法进行清理。'"
  }
];
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        let score = 0;
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          optionsListEl.innerHTML = '';
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            nextBtn.style.display = 'block';
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            nextBtn.disabled = false; // 最后一题时，下一题按钮不禁用，而是用于显示报告
            nextBtn.textContent = (currentQuestionIndex === quizData.length - 1) ? '查看报告' : '下一题';
            
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            if (!quizData[currentQuestionIndex].hint) {
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        function showResult(isCorrect, questionData) {
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            resultBox.className = `result-box ${isCorrect ? 'correct' : 'incorrect'}`;
            
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            }
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            html += `<div class="source-text">来源: ${questionData.source}</div>`;
            
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                // 高亮正确答案
                if (index === questionData.correctAnswerIndex) {
                    child.classList.add('correct'); // 需要添加CSS样式
                    child.style.backgroundColor = '#d4edda';
                    child.style.borderColor = '#c3e6cb';
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            document.getElementById('quiz-footer').style.display = 'none';

            const correctCount = score;
            const totalQuestions = quizData.length;
            const answeredCount = userAnswers.filter(a => a !== null).length;
            const wrongCount = answeredCount - correctCount;
            const skippedCount = totalQuestions - answeredCount;
            const accuracy = totalQuestions > 0 ? Math.round((correctCount / totalQuestions) * 100) : 0;
            const errorRate = totalQuestions > 0 ? Math.round((wrongCount / totalQuestions) * 100) : 0;

            const finalScoreHtml =
                '<div class="final-score-container">' +
                '<h2>答题报告</h2>' +
                '<div class="score-summary">' +
                '<div class="score-card">' +
                '<h3>得分</h3>' +
                '<p>' + correctCount + ' / ' + totalQuestions + '</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>正确率</h3>' +
                '<p>' + accuracy + '%</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>错误率</h3>' +
                '<p>' + errorRate + '%</p>' +
                '</div>' +
                '<div class="score-card score-details">' +
                '<table>' +
                '<tr><td>正确</td><td>' + correctCount + '</td></tr>' +
                '<tr><td>错误</td><td>' + wrongCount + '</td></tr>' +
                '<tr><td>未答</td><td>' + skippedCount + '</td></tr>' +
                '</table>' +
                '</div>' +
                '</div>' +
                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  